The IEEE 802.21 standard provides a uniform set of functionalities that help enable and enhance handovers across different link layer technologies. IEEE 802.21 defines three main services available to Mobility Management applications, such as Client Mobile Internet Protocol (Client MIP) or Proxy MIP. Referring to FIG. 1, these services are the Event Service 100, the Information Service 105 and the Command Service 110. These services aid in the management of handover operations, system discovery and system selection by providing information and triggers from lower layers 115 to upper layers 120 via a media independent handover (MIH) function (MIHF) 125.
At a high level, this involves an upper layer MIH User which can communicate with an MIH Function 125 (either locally or remotely over some transport medium) through link-independent Event Service 100, Information Service 105 and Command Service 110. The MIH Function 125, in turn, will interact with link-layer devices through the use technology-specific primitives; the functionalities expected from these technology-specific primitives are defined in the 802.21 standard. While FIG. 1 shows MIHF 125 as a middle layer in a protocol stack, MIHF 125 may also be implemented as an MIH plane that is capable of exchanging information and triggers directly with different layers of the protocol stack.
The Third Generation Partnership Project (3GPP) has identified three principles that describe how inter-system handovers between 3GPP and non-3GPP access (e.g. 3GPP2, IEEE 802.11 WLAN, IEEE 802.16 WiMAX, etc.) should be handled. However, these principles do not address how two different accesses can be integrated in order to allow handover execution. The first principle applies in multiple RAT scenarios where the wireless transmit/receive unit (WTRU) uses a single radio access technology (RAT) for all in-progress services. The second principle is that the Inter-RAT handover decision is made and the handover command is sent by the serving Radio Access Network (RAN). The target RAN may exercise admission control to the WTRUs that are handed over. The third principle is that the serving RAN receives information from the target RAN that can be included in the handover command.
All these principles can be met by using the handover (HO) service provided by the 802.21 standard. This is especially needed when handover commands requesting a switch over toward or from a 3GPP based access is required, for example, when a handover takes place between IEEE 802.16 or WiMAX accesses and 3GPP accesses, or between IEEE 802.11 or WLAN systems and 3GPP systems.
FIG. 2 depicts a typical GSM Edge Radio Access Network—UMTS Terrestrial Radio Access Network (GERAN-UTRAN) 3GPP packet switched (PS-domain) Inter-RAT architecture 200. Referring to FIG. 2, the source network includes a serving GPRS support node SGSN 205, a base station controller/radio network controller (BSC/RNC) 210, and a base transceiver station (BTS)/Node B 215. The BSC/RNC 210 communicates with the SGSN 205 through a Gb/IuPS interface 220. In addition, the BSC/RNC 210 communicates with the BTS/Node B 215 through an Abis/Iub interface 225. The target network includes a SGSN 230, a BSC/RNC 235, and a BTS/Node B 240. The BSC/RNC 235 communicates with the SGSN 230 through a Gb/IuPS interface 245. The BSC/RNC 235 communicates with the BTS/Node B 240 through an Abis/Iub interface 250. The source and target SGSNs 205,230 communicate through a Gn interface 255.
Referring to FIG. 2, it is the source BSC/RNC 210 that controls the handover. The mobile node (MN) 260 is requested to take measurements in the target network and, upon meeting the handover conditions, the source BSC/RNC 210 requests the target BSC/RNC 235 to prepare the resources for the MN 260. The target BSC/RNC 235 performs admission control and responds with the new resource allocation. Once the new resources have been allocated, the source BSC/RNC 210 commands the MN 260 to handover to the new network. Upon detecting the MN 260 in the new network, the target BSC/RNC 235 informs the source BSC/RNC 210 of the handover completion.
In order to perform heterogeneous handover between a 3GPP and non-3GPP network, the network architecture must provide capability for an MIH User to acquire measurement reports and capability for an MIH Function to reserve link layer resources through the use of standardized MIH primitives and messages. While the 802.21 standard provides mechanisms to obtain such measurement reports, query for resources, reserve these resources, execute the handover and inform the peer network about the completion of the action, the mechanisms have deficiencies that deprive implementers from the use of key functionalities and from complete control of the measurement-reporting process. This is specifically true for handover between 3GPP (e.g. GERAN, UTRAN and LTE) and non-3GPP networks, which are also known as Inter-Radio Access Technology (Inter-RAT) handovers.
When two peer networks are to perform a handover, typically based on Mobile Node (MN) (also referred to as User Equipment or UE) measurement reports, the network instructs the MN to switch to another cell and indicates what configuration to use in the new cell. This implies that the Inter-RAT handover decision is made by the serving Radio Access Network (RAN), whereas the target RAN may exercise admission control on the MN that is being handed over.
Hence, the sequence of events is 1) a Query phase used to determine the status of resources at both source and target networks before taking a handover decision, 2) a Preparation phase where resources are reserved at the target network once a handover decision has been taken, 3) an Execution phase when the handover commands are sent and performed, and 4) a Completion phase when the result of the handover is informed and the original resources are released.
The IEEE 802.21 specification defines messages that can be used to perform the actions described above. However, the functionality provided by the currently defined messages is insufficient to convey all the required information between source and target networks, especially in the case of 3GPP to non-3GPP handover (and vice versa). It would therefore be desirable to provide messages to convey all the required information between source and target networks without compromising functionality. In order to perform heterogeneous handover between a 3GPP and non-3GPP network, it would also be desirable to design a network architecture to provide capability for an MIH User to acquire measurement reports and capability for an MIH Function to reserve link layer resources through the use of standardized MIH primitives and messages.